Update our CMake code to handle Policy53.

Policy 53 deals with the new simplified parser logic added to CMake in 3.1 .
The policy detector has a couple of false positives with Remus as we
set-up strings for configuration, so we enable the policy when we can to
suppress these false positive warnings.
Update our version of kwsys to correct CMake Policy 53 and 54 warnings.
Merge pull request #176 from robertmaynard/cmake_policy_53

Cmake policy 53